I don't think it is your age. Very likely it is the employment gap. I would also expect BSc may not be good enough now to get a "scientist" position (you may be competing against MScs and PhDs and in Singapore degrees matter).
Some general comments as you did not put down too many details:
If you applied for a lab supervisor position you may need some upgrading as a lot happened from legal-safety perspective in past decade. In this case I would try to take some of the WDA courses (
http://www.wda.gov.sg, browse and see what may suit you). As a PR you should be able to get some subsidy. This should IMO significantly increase you chances.
If you applied for a research position:
1) If you are in biosciences you probably have lower chances to get a job as this area has been developing very rapidly and you are left far behind.
2) If any other area of natural sciences (material, chemistry related etc., testing and characterization) you would still fit with no problem but need to convince your potential employer that the gap does not affected you.
I guess your science days were still outside Singapore (in Malaysia)? Regardless, maybe you could contact your last employer and if positive, even consider a temporary (1year) emigration to get some bridging experience?
In every single case when you apply for a position contact your potential future boss directly. Find her/his phone number and call her/him. This is always a correct approach but it is IMO crucial in your case for the reasons I mentioned in my previous post - you should be able to win a lot taking and communicating directly as opposite to sending some formal CV.